In many applications the mechanical, chemical or physical properties of surfaces of materials are important. If such surface properties are not provided by the bulk properties of the material, the application of coatings and surface modification are convenient ways of improving surface properties such as hardness, chemical resistance, electrical resistivity, barrier properties and optical appearance. Conventionally, the application of such coatings or surface modification is often performed at reduced pressures using methods such as sputtering, vacuum deposition or ion plating. However, the realisation of continuous production of such coatings or surface modification is difficult to realise at reduced pressure. Atmospheric plasma treatment processes have been proposed to overcome these problems in which a layer with the required physical and/or chemical property is formed on the surface of a substrate with a uniform composition or the surface itself of a substrate is modified.
U.S. 2002/0057999A1 discloses an installation in which an operation is performed that requires control over the atmosphere inside a chamber (3), the operation being performed in the presence of a gaseous mixture capable of giving off emissions, characterized in that it comprises: inlet and outlet devices (5, 8) adjoining the chamber to oppose respectively the ingress of air into the chamber and the exit of gaseous emissions therefrom; an extraction device (4) comprising a duct opening into the chamber; and means (42) for regulating the flow rate of gas drawn out by said extraction device so as to maintain an approximately zero pressure difference between the inside of the chamber and the surrounding atmosphere.
U.S. 2003/0113479A1 discloses an atmospheric pressure plasma treatment apparatus comprising a first electrode and a second electrode opposed to each other in which a discharge space is formed between the opposed electrodes, a voltage application device for applying voltage across the discharge space, a gas supply device for supplying a reactive gas and an inert gas to the discharge space, wherein the reactive gas at the discharge space is excited at atmospheric pressure or at approximately atmospheric pressure by applying voltage through the voltage application device to generate discharge plasma, and a substrate is exposed to the discharge plasma to be subjected to surface treatment, and wherein the reactive gas is not directly in contact with the discharge surface of the first electrode or the second electrode.
U.S. 2004/0050685A1 discloses a method for plasma treatment under atmospheric pressure for treating an article to be treated comprising: providing a solid dielectric on at least one opposing face of a pair of opposing electrodes under pressure near the atmospheric pressure; introducing a treatment gas between said a pair of opposing electrodes; generating plasma by applying an electric field between said electrodes; and contacting the plasma with the article to be treated, wherein an used gas is exhausted from the vicinity of treatment section where said plasma and said body to be treated are in contact, and said vicinity of treatment section is maintained under a specified gas atmosphere by a gas atmosphere control mechanism.
U.S. 2004/0050685A1 further discloses an equipment for plasma treatment under the atmospheric pressure comprising: a pair of opposing electrodes with a solid dielectric being provided on at least one opposing face thereof; a mechanism for introducing a treatment gas between said pair of opposing electrodes; a mechanism for applying an electric field between said electrodes; a mechanism for contacting the plasma obtained by said electric field with said article to be treated; a mechanism for exhausting an used gas; and a mechanism for maintaining the vicinity of treatment section, where said plasma and said article to be treated are in contact, under the specified gas atmosphere.
WO 2004/028220A1 discloses a method for generating and maintaining a plasma according to the Dielectric Barrier Discharge (DBD) technique, said method comprising the steps of: introducing a sample in the space between two electrodes, a mixed atmosphere being present between said electrodes, applying an alternating voltage to said electrodes for generating and maintaining a plasma in the volumetric space between the electrodes preferably at a pressure in the range between 100 Pa and 1 MPa, said voltage having a profile as a function of time, defined by a sequence of time periods during which a positive or zero voltage is applied, alternated with time periods during which a negative or zero voltage is applied, characterized in that said profile is asymmetrical with respect to amplitude and/or time.
WO 2005/098007A1 discloses a method for coating a substrate with an inorganic-organic hybrid polymer material using the Dielectric Barrier Discharge (DBD) technique, said method comprising the steps of: a) introducing a sample in the space between two electrodes, b) controlling the atmosphere between the electrodes, c) generating a plasma discharge between the electrodes, d) mixing aerosols containing hybrid organic/inorganic cross-linked pre-polymers formed via sol-gel processing, into the plasma discharge.
WO 2006/081637A1 discloses a plasma jet apparatus for performing plasma processing of an article, comprising: an elongated central electrode, an elongated cylindrical outer electrode surrounding said central electrode and being coaxial with said central electrode, an electrical insulator coaxially disposed between said outer electrode and said central electrode, wherein a discharge lumen having a distal end and a proximal end is defined between said central electrode and said electrical insulator, a supply opening disposed at said distal end of said discharge lumen for supplying a plasma producing gas to said discharge lumen, a power source for providing a voltage between said central electrode and said outer electrode characterised in that said electrical insulator extends in a radially placed ring at said proximal end beyond the outer surface of said outer electrode.
WO 2006/116828A1 discloses an apparatus for disinfection and purification of a medium comprising a liquid, gaseous or solid phase, or a mixture thereof, said apparatus comprising: a central electrode, a dielectric layer adjacent to said electrode, a first area adjacent to said dielectric layer, and means to introduce a first medium into said first area, a second area adjacent to said first area, and means to introduce a second medium into said second area, a means for creating a plasma in said first medium, while said first medium is present in the first area, by applying a voltage between said first electrode and a second electrode, a means for injecting said plasma into the second area, in order to be mixed with the second medium.
U.S. 2007/0202270A1 further discloses a method for coating a substrate with an inorganic-organic hybrid polymer material using the Dielectric Barrier Discharge (DBD) technique, said method comprising the steps of: a) introducing a sample in the space between two electrodes, b) controlling the atmosphere between the electrodes, c) generating a plasma discharge between the electrodes, d) mixing aerosols containing hybrid organic/inorganic cross-linked pre-polymers formed via sol-gel processing, into the plasma discharge.
WO 2007/053916A1 discloses a method for producing a coating comprising a conjugated polymer on a substrate, comprising the steps of: providing a substrate, introducing a conjugated polymer coating forming material into an atmospheric pressure plasma discharge, or into the reactive gas stream resulting therefrom, simultaneously with the introduction of a coating forming material, introducing an additional material into said plasma discharge or the reactive gas stream resulting therefrom, exposing the substrate to said plasma discharge or the reactive gas stream resulting therefrom, thereby obtaining said coating.
WO 2008/119823A1 discloses a method of coating a substrate, said method comprising the steps of: providing a substrate, producing an atmospheric pressure plasma discharge in the presence or a gas, at least partially exposing the substrate to said atmospheric pressure plasma discharge, introducing a liquid aerosol of coating forming material into said atmospheric pressure plasma discharge, thereby forming a coating on the substrate, curing the substrate and the coating, by exposing the substrate to ultraviolet light.
D. Vangeneugden et al. in the “Proceedings of the 10th Asian Textile Conference—ATC-10- Sep. 7-9, 2009 at Ueda, Japan” reported that low temperature atmospheric pressure plasma by means of dielectric barrier discharges (DBD) constitutes an emerging technology for surface pre-treatment and coating and extended the variety of chemical precursors used in DBD deposition processes from gases and liquids with high vapour pressures and/or high stability to include nano-sized aerosols.
U.S. 2009/0120782A1 discloses a surface treater, comprising: a support for supporting a material passing through the treater; an active electrode having a discharge surface disposed opposite the support; a roller disposed proximate to the active electrode to define a discharge chamber between the support and the roller in which the discharge surface of the active electrode is disposed; and a high voltage power supply operatively connected to the active electrode to ionize a process gas and produce a discharge within the discharge chamber, wherein the roller sealingly engages the material to confine the discharge chamber. U.S. 2009/0120782A1 also discloses a process for surface treatment of continuous web materials, the process comprising: supporting a web material on a support; creating a discharge chamber between the support and at least one roller; disposing a discharge surface of an active electrode within the discharge chamber; passing the web material into the discharge chamber; confining the discharge chamber at the interface with the web material by contacting the web with the at least one roller; energizing the active electrode with high voltage to ionize process gas within the discharge chamber to create a discharge through which the web material passes.
JP 2001-279457A discloses a continuous surface treating method of a continuous film deposition method using atmospheric pressure plasma for performing discharge plasma treating under a pressure under an almost atmospheric pressure in a gaseous mixture atmosphere, wherein electrodes provided with opposed each other at a predetermined discharge interval supply a gaseous mixture between roll-shaped discharge plasma treating electrodes to perform the discharge plasma treating. The substrate is a film. JP 2001-279457A in FIG. 1 discloses the simultaneous roll to roll coating of two films moving in the same direction between two roll-shaped discharge plasma electrodes with the discharge in the space between the two continuous films.
JP 2007-073333A discloses a plasma discharge treatment apparatus, comprising: a pair of electrodes; gas supplying means supplying at least a discharge gas to a facing region of the electrodes; a high frequency power supply supplying high-frequency electricity to at least one of the electrodes and generating plasma discharge in the facing region of the electrodes; and substrate belt conveying means conveying a substrate belt to the facing region of the electrodes, wherein the apparatus includes an electrode moving means which moves at least one of the electrodes in parallel in a direction perpendicular to a conveying direction of the substrate belt with respect to the other electrode. JP 2007-073333A in FIG. 1 discloses the continuous roll to roll coating of a single film in two passes between two roll-shaped discharge plasma electrodes with the discharge in the space between the continuous film as it passes through in opposite directions.
JP 2007-332426A discloses a film deposition method characterized in that it comprises the plasma generation operation wherein the outer circumferential surface of a rotary electrode having cylindrical outer circumferential surface is arranged to face the surface of the base material made from an insulating material by keeping a space or, the said outer circumferential surface is arranged to face the counter component by keeping a space and generating plasma in the space, and the operation of conveying the said base material in the direction almost perpendicular to the direction of rotation of the axis of the said rotary electrode in the vicinity of the plasma formation region and, operation of supplying gas wherein the gas in the vicinity of the outer circumferential surface of the said rotary electrode is supplied to the said plasma generation region by dragging-in the gas by rotating the said rotary electrode around the axis at the centre of the outer circumferential surface to induce chemical reaction in the said gas by means of the energy of the plasma, to form a film on the surface of the said base material. Moreover, in the said plasma generation operation, the plasma is generated in a region situated at a position shifted to the upstream side in the direction of rotation of the rotary electrode with respect to the said position of said minimum space. Furthermore, JP 2007-332426A in FIG. 3 shows an almost flat electrode as a counter electrode in place of the earthed roller for conveyance, the electrode conveyor belt. The electrode that serves as counter electrode of the rotary electrode has a flat electrode plate which is almost parallel to the said base material and is situated on the back side of the conveyor belt made from an insulator-like rubber and acting as the means of transport of the base material.
WO 2009/104579A1 discloses a plasma discharge device comprising opposing electrodes consisting of a pair of rotating roll electrodes, a plasma discharge space wherein a voltage is applied between the opposing electrodes to generate a plasma discharge, a substrate that passes through the plasma discharge space while being held by said opposing electrodes that consist of roll electrodes, and a process gas supply means that supplies process gas into said plasma discharge space, wherein said process gas is composed of a discharge gas and a thin film-forming gas, said discharge gas containing at least 90 vol % or more of nitrogen gas, and the ratio of the diameters of the above pair of roll electrodes that constitute said opposing electrodes is 1.00:0.55 to 1.00:0.95. WO 2009/104579A1 further discloses that the substrate is preferably transported consecutively using a loop transportation method to form a functional film on said base material. The loop is formed by the substrate film itself. WO 2009/104579A1 in FIGS. 1, 3, 7, 10 and 11 discloses the continuous roll to roll coating of a single film in two passes between two roll-shaped discharge plasma electrodes with the discharge in the space between the continuous film as it passes through in opposite directions. WO 2009/104579A1 in FIGS. 5 and 8 discloses the forming of a film on a single endless loop in two passes in opposite directions between two roll-shaped discharge plasma electrodes with the discharge in the space between endless loop as it passes in opposite directions between the electrodes. WO 2009/104579A1 in FIG. 6 discloses the transport of endless loops round each of two roll-shaped discharge plasma electrodes each moving in opposite directions with the discharge in the space between the two endless loops as they pass between the electrodes with a film being formed simultaneously on different substrates. However, WO 2009/104579A fails to disclose the continuous coating of a web material transported by endless dielectric belts.
WO 2008/065861A discloses an atmospheric plasma processing apparatus capable of forming a thin film having high uniformity on a cylindrical substrate stably and with high productivity. The atmospheric plasma processing apparatus has at least two substrate carrying units each holding the cylindrical substrate by a roll electrode and a guide roll and disposed at positions opposing each other. A gas containing a thin film forming gas is supplied to a discharge space formed between the opposing roil electrodes under an atmospheric pressure or a pressure near the atmospheric pressure, and a high-frequency electric field is applied to the discharge space, thereby exciting the gas. At least the two cylindrical substrates are exposed to the excited gas, so that thin films are simultaneously formed. These ‘cylindrical” substrates 175 are in fact an endless substrate forming a cylindrical surface by spanning round the roll electrode 20a and the driven roller 201 (see paragraph [0020]), Paragraphs [0112] and [0113] are silent in respect of the cleaning of the substrate. WO 2008/065861A fails to disclose the continuous coating of a web material transported by endless dielectric belts.
U.S. 2004/045806A1 discloses a method for treating the surface of objects, in particular made of strip material or of deep-drawn material, in which the to-be-treated surface (2) of the object (1) is subjected in a discharge region (3) filled with a first gas or gas mixture to a barrier discharge generated between a first planar electrode (4) and a second planar electrode (5), wherein a plasma-excited second gas or gas mixture emitting UV radiation to which said to-be-treated surface (2) is additionally subjected is provided as said second electrode (5). U.S. 2004/045806A fails to disclose the continuous coating of a web material transported by endless dielectric belts.
Plasma treatment at or near atmospheric pressure involving one or more roll electrodes has the advantage of precise parallelism of the gap between the electrodes, but the disadvantage of a very short coating zone due to the shape of the roll electrodes. Moreover, inhomogeneous treatments may be produced in the case of two pass-coating, if the passes are in opposite directions.